Wis. Stat. § 64.01: How to organize under ss. 64.01 to 64.15.

(1) Any city of the second, third or fourth class may reorganize under the provisions of ss. 64.01 to 64.15, either by enactment of a charter ordinance or by a petition and referendum election as provided by s. 66.0101. Such petition and election shall be governed by s. 9.20 (1) to (6).

(2) When adopted in the manner hereinbefore provided, the provisions of ss. 64.01 to 64.15 shall take effect and become operative on the third Tuesday in April.

(3) Any village qualified under s. 61.189 to become a city may organize under ss. 64.01 to 64.15 by the adoption of a charter ordinance or by a petition and referendum election as provided by s. 66.0101. Such petition and election shall be governed by s. 9.20 (1) to (6).